It has become increasingly common for users of personal computers (PC) to view video content via a PC. Video content is sent to a user's PC compressed (i.e. the quantity of data used to represent the video content is reduced without an excessive reduction in quality) and a video codec (a computer program that encodes and decodes video data) installed on the PC decodes (i.e. decompresses) the video data and sends the decoded/uncompressed content to the video card, which outputs the content to a display.
Unlike a consumer electronics (CE) device, which is a closed box where users cannot load software onto the box or add hardware to capture content, a PC is an open platform and cannot be trusted. There is therefore increasing concern about the piracy of video content that is decoded by and viewed via a PC.
In a Microsoft White Paper entitled “Output Content Protection and Windows Vista” (Dave Marsh, WinHEC 2005 Version, Apr. 27, 2005), methods are described that aim to make a Windows Vista based PC a safer place for content so that content providers will be happy to allow Windows Vista based PCs to play their content. The PC's software decoder resides in a ‘protected environment’—a set of components, guidelines and tools that provides a ‘wall’ against outside attacks, where within the wall, content can be processed without undue risk of it being stolen. Also, uncompressed video is encrypted before being sent from decoder to video card over a user-accessible bus by Protected Video Path—User Accessible Bus (PVP-UAB) encryption.
However, decoding in software, even if secured within a protected environment, is still a weak link because decrypted, compressed video data, decrypted uncompressed video data and secret keys are stored in computer memory before PVP-UAB encryption is applied and can therefore be found and copied.
It is much better to decode video data in a secure hardware component and have the secure hardware component output uncompressed, encrypted video over a secure channel so that decrypted, compressed video data; decrypted, uncompressed video data; and secret keys are not accessible by the PC processor in the clear.
However, this requires the secure hardware component to output vast amounts of uncompressed video data, which requires lots of bandwidth and processing power. Universal Serial Bus (USB) and other peripheral device buses are not fast enough and even if they were, this would require a significant amount of bus resources. The problem is also much worse for High Definition (HD) video data, which contains up to six times as many pixels as Standard Definition (SD) video data.
International patent application WO02/079955 to NDS Limited (also published as US 2004-0111613) describes a system and a method for providing variable security mechanisms for securing digital content, in which a single security mechanism is not used for all content Instead, at least one characteristic or feature of the security mechanism is varied between units, instances or categories of content.
The disclosures of all references mentioned above and throughout the present specification, as well as the disclosures of all references mentioned in those references, are hereby incorporated herein by reference.